Hyperthermia as a modality for the treatment of numerous types of cancers continues to show promise for clinical use, especially when used synergistically with low dosage x-rays. Methods of heat deposition include microwave, RF, and ultrasound. To date, all suffer in not being able to deposit the correct amount of heat to the tumor site with minimal interference to normal tissue in an accurate and controlled fashion. As a result, hyperthermia treatment of deep tumors has been largely ignored. A scanning focused beam ultrasound hyperthermia delivery system has been developed by the proposers for the treatment of deep tumors. At present, this system features temperature monitoring within the tumor volume using thermocouples, flying spot heating, and continuous recording of important parameters. Critical for the successful implementation of this system is the development of models which can provide in real time 3-D temperature profiles. These models must include temperature data at selected points, and provide for real time feedback control by intensity modulation of the ultrasonic beam. The method of attack under development is to adopt simple models which retain the basic heat transfer processes and geometry and yet allow approximate techniques, such as the method of weighted residuals, to be applied for the solution. Considerable attention will be placed on handling blood flow and the power source term which becomes temperature dependent by virtue of the feedback control. Progress to date indicates the approach to be sound. The research proposed in phase I is crucial for the successful implementation of a sophisticated hyperthermia delivery system for clinical use. Simple 1-D models already developed by the researchers will be extended to 3-D and to geometries more representitive of in vivo tumors. The new hyperthermia system will be clinically evaluated during Phase II.